The present invention relates to an improved process for preparing tetraalkyl-biphenols by the reaction of a di(lower alkyl)-substituted phenol with a peroxidase enzyme and peroxide, and, more particularly, by the reaction of 2,4- or 2,6-dimethylphenol in the presence of soybean peroxidase and hydrogen peroxide.
Commercial reactions for preparing tetraalkyl substituted diols are known, however, the reactions are undesirable because they are inefficient and extremely inconvenient to carry out in an industrial setting. For example, Japanese Kokai Tokyo Koho JP 04338347 AZ describes the preparation of 3,3',5,5'-tetramethyl-4,4'-biphenol in little over 60% yield by oxidative dimerization of appropriate phenols in a molten state in the presence of an oxygen-containing gas and sodium hydroxide. The reaction product contained greater than 35% unwanted monomer. Japanese Kokai Tokkyo Koho JP 03275639 AZ describes the oxidative coupling of 2,6-xylenol in the presence of copper acetate, sodium bicarbonate, sodium dodecyl sulfate and sodium sulfate to give 3,3',5,5'-tetramethyl-4,4'-biphenol. Japanese Kokai Tokkyo Koho JP 03275638 AZ describes the preparation of 3,3',5,5'-tetramethyl-4,4'-biphenol by the oxidative dimerization of 2,6-xylenol in the presence of metal catalysts such as copper acetate. The prior art reactions are undesirable because they are generally inefficient and the metals or metal salts must be removed and either recycled or properly disposed of. Accordingly, there exists a need for a convenient and inexpensive method for preparing tetraalkylbiphenols from di(lower alkyl)substituted phenols.